Wireless capacity planning for a trade show

I'm exploring options for a temporary wireless network setup for a decent-sized trade show. I'm considering pfSense for this, but wanted to poll others here with some basic questions to see if the specs I'm looking for seem feasible. Here's the general setup:

One exhibition hall approximately 300' x 450' with a 35' ceiling

500-600 potential wireless users

The wireless network would not provide Internet access or access to other wireless clients–it would only provide connection to a central web-based ordering system running on a server onsite over SSL.
(A separate for-pay wireless network with Internet access is provided by another party, on different networking hardware altogether)

For quick setup and for easier portability, I'd like to run on a small form factor (embedded version) and not run cables between access points – using WDS or OLSR instead.

I expect wireless coverage and interference issues to be the biggest challenges, since the bandwidth and routing requirements for the web app are minimal.

Would a bunch of WRAP boards with Atheros cards running pfSense seem like a feasible option for this?

Does running the full PC version give the capacity to support more wireless users, or is this a function of the radio on the wireless card rather than the CPU/RAM?

For those familiar with DD-WRT or OpenWRT, does pfSense on the WRAP potentially support more wireless users than the Linksys or Buffalo broadcom devices running one of the WRT variants?

Does OLSR with pfSense make sense for an indoor setup like this with no WAN connections, only one LAN with the web server/servers?

I have pfSense running in quite a few locations on full PCs with attached separate access points, but haven't experimented yet with the embedded version or with internal wireless cards. I know of full-blown commercial solutions for this like this one from Strix systems: http://www.strixsystems.com/solutions/tempnetworks.asp , but I'd prefer to stick with pfSense if it seems feasible.